/*
 * @Author: long-xinyu2 2192763423@qq.com
 * @Date: 2025-03-19 15:23:54
 * @LastEditors: long-xinyu2 2192763423@qq.com
 * @LastEditTime: 2025-03-19 15:46:45
 * @FilePath: \algorithm\algorithm-training\2025牛客寒假2\d.cpp
 * @Description: 这是默认设置,请设置`customMade`, 打开koroFileHeader查看配置 进行设置: https://github.com/OBKoro1/koro1FileHeader/wiki/%E9%85%8D%E7%BD%AE
 */
#include<iostream>
#include<cstring>
#include<vector>
#include<map>
#include<cstdio>
#include<algorithm>
#include<string>
#include<string.h>
#include<queue>
#include<math.h>
#include<set>
#include<functional>
using namespace std;
using ull = unsigned long long;
#define int long long
//using i128 = __int128_t;
inline int inc(int x, int v, int mod) { x += v;return x >= mod ? x - mod : x; }//代替取模+
#define endl '\n'
typedef long long LL;
typedef unsigned long long ULL;
typedef pair<int, int> PII;

const int N = 2e3 + 10, M = 1e5 + 10;

inline int read()
{
    int x = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9')
    {
        if (ch == '-')
            f = -1;
        ch = getchar();
    }
    while (ch >= '0' && ch <= '9')
        x = x * 10 + ch - '0', ch = getchar();
    return x * f;
}

void solve()
{
   int n;
   cin >> n;
   string s;
   cin >> s;
   set<char>sp;
   int ans = 0;
   for(int i = s.size() - 1; i >= 1; i --)
   {
       if(sp.find(s[i]) == sp.end()) sp.insert(s[i]);
       else 
       {
            ans = max(ans,i + 1);
       }
   }
   sp.clear();
   for(int i = 0; i <= s.size() - 2; i ++)
   {
        if(sp.find(s[i]) == sp.end()) sp.insert(s[i]);
        else 
        {
            ans = max(ans,(int)s.size() - i);
        }
   }
   cout << ans << endl;
}
signed main()
{
    ios::sync_with_stdio(0);
    cin.tie(0);
    int tt;
    //cin >> tt;
    tt = 1;
    while (tt--)
    {
        solve();
    }
}